1- a) Describe clearly how to calculate the present value of an annuity using two perpetuities with different starting points in time. b) Present value of an annuity can be calculated by using the below formula where C is the cashflow per period; r is the discount rate; and t is the lifetime of annuity. Explain what does this formula incorporate (for example why do we have 1/r or 1/(r1+r)t) in the formula). PVofannuity=C[r1r(1+r)t1]